This invention relates to a heat exchanger construction. More specifically, this invention relates to a heat exchanger core including a design which increases the heat exchange surface area for a given volume.
Heat exchangers in general are well known in the prior art, and typically comprise a heat exchanger core having dual fluid flow paths for passage of two fluids in heat exchange relationship with each other without intermixing. In one common form, such heat exchangers typically comprise a plurality of relatively thin divider plates arranged in an alternating stack with a plurality of extended surface heat transfer elements, such as corrugated fins and the like. The extended surface heat transfer elements, or fins, are commonly turned alternately at right angles with respect to each other to define two closely adjacent fluid flow paths for passage of the two working fluids at right angles to each other. This construction is commonly known as a cross flow heat exchanger, and includes appropriate header bars along side margins of the stack to isolate the two working fluids from one another. When the stack is assembled, the various components thereof are commonly secured together preferably in a single bonding operation, such as brazing or the like.
Heat exchangers further require some type of manifold or header structure for guiding at least one of the working fluids for ingress and egress with respect to its associated flow path through the heat exchanger core in isolation from the other working fluid. For example, when the heat exchanger is used to transfer heat energy between a liquid and a gas, the liquid is normally supplied through an appropriate inlet conduit to an inlet manifold connected to the heat exchanger core. The inlet header guides the liquid for flow into and through one of the flow paths in the core in heat transfer relationship with the gas which typically flows freely without headers through the other core fluid flow path. An outlet header connected to the heat exchanger core collects the liquid discharged from one of the fluid flow paths for passage away from the heat exchanger through an appropriate outlet conduit.
Manufacturers of vehicles employing internal combustion engines generally dictate the size and location of under-the-hood accessories supplied by manufacturers of these accessories. Therefore, once the particular space limitations are placed upon the supplier, it is of utmost importance to design a component which fits within that space limitation and meets the vehicle manufacturer's performance requirements. In the case of heat exchangers, once given the space limitations on the heat exchanger, it is important to maximize the heat and weight transfer characteristics in order to minimize the size of the overall heat exchanger. In order to accomplish this, it is necessary to maximize the cooling of the hot liquid coolant exiting the engine.
A common problem with the heat exchangers of the prior art rests in their design of the liquid core flow path. More specifically, these heat exchangers utilize a solid header bar on either side of the corrugated fins to define the core fluid flow path. As such, these solid bars do not provide a maximization of the heat transfer between the hot liquid flowing through the flow path defined by these solid bars and the cooler gas flowing in cross-flow relationship thereto. The solid bars also contribute to substantial weight penalties.
The present invention overcomes the problems and disadvantage of the prior art heat exchangers by providing an improved heat exchanger construction including tubes which eliminate the need for solid bars and more importantly maximize the fin density within the core passage.
In accordance with the present invention, a heat exchanger comprises a heat exchanger core defining a pair of fluid flow paths for passage of a pair of working fluids in heat transfer relationship with each other and integrally mounted inlet and outlet headers for guiding one of the working fluids into and through one of the flow paths in isolation with the other fluid.
Each fluid flow path is actually made of a plurality of smaller flow paths. The first or hot fluid flow path is defined by a plurality of tubes which are spaced apart from the adjacent tube by two formed header bars. The second or cool fluid flow path is defined by a plurality of cross-flow spaces between the plurality of tubes and the formed header bars. Generally, the end passages of the core are cross-flow spaces and require solid end plates to define the outermost boundaries of the cross-flow space.
Each tube comprises two identically formed members which are complementary to each other. More specifically, the tubes are generally U-shaped having an elongated base section and upright legs on each side of the base section. One leg of each of the members is folded back over itself twice. The first and second folds are spaced apart from one another thereby forming a trough which runs the length of the member. The two identically formed complementary members are then placed one on top of each other with the non-folded end of each member being inserted to the trough of its complementary member. Assembled in this manner, the two pieces form a fluid fluid core flow path therebetween. Inserted between the two members either before or after assembly thereof is a corrugated heat transfer element fin. Tubes formed in this manner are alternated with formed header bars running at right angles thereto.
The formed header bars define the boundary width of each of the smaller second flow paths. The formed header bars are generally C-shaped in cross section and include a lanced tab extended from its central portion at each horizontal end thereof. The tabs at each end of the bars are folded inward and over itself. Inserted between the two formed header bars during assembly of the heat exchanger core is a corrugated heat transfer fin element. The spaced bars thereby define the width of the second flow path while the two tubes spaced by the bars define the height of the second small passages. Once the desired number of tubes and pairs of formed header bars have been stacked, side plates are placed over the exposed extended surface heat transfer elements of the cross-flow path. Headers are then attached to the core ends to which the first fluid flow paths are open.
It is an object of this invention to provide a heat exchanger core design which maximizes the heat exchanger fin density for a given volume.
It is another object of this invention to provide a lightweight, compact heat exchanger.
It is another object of this invention to provide an heat exchanger core which is easy to assembly.